1. Field of the Invention
The present invention relates to a transparent electromagnetic radiation shielding sheet, a method of producing the same and a display device using the same. More particularly, the present invention relates to a transparent electromagnetic radiation shielding sheet that has sufficient visible light transmittance and electromagnetic radiation shielding performance and that is also light, excellent in durability and is favorably used in various display devices. Further, the present invention relates to a method of producing such transparent electromagnetic radiation shielding sheet. Furthermore, it relates to a display device such as a plasma display device and a CRT (cold-cathode ray tube) having the transparent electromagnetic radiation shielding sheet placed on the front surface of a display panel of the display device.
2. Discussion of the Related Art
It has been noted that electromagnetic radiation is generated from the surface of a display panel of a plasma display device, a CRT device, etc. In recent years, the interference with other devices and the influence of the electromagnetic radiation on human health caused by this electromagnetic radiation has become an issue.
To shield such electromagnetic radiation, a transparent electromagnetic radiation shielding sheet has been widely used for attachment to or placement on the front surface of a display panel. Examples of such transparent electromagnetic radiation shielding sheets include ones that are produced by a method such as (1) laminating a transparent conductive film having indium oxide, tin oxide, silver, etc. on a plastic transparent base material (International Patent Publication No. 98/13850), (2) integrally laminating a synthetic fiber fabric such as polyester having a copper/nickel thin film layer which is coated on the surface thereof on a transparent base material (Japanese Patent Application Laid-Open No. 8-183132 (JP 8-183132), (3) integrating a synthetic fiber fabric such as polyester having a copper/nickel thin film layer coated on the surface thereof to be intervened between two sheets of glass plate (JP 11-74684), (4) laminating a mesh-like conductive material and a glass or plastic transparent base material with a hot melt adhesive resin therebetween (JP 2001-77587) and (5) patterning a conductive mesh on a glass or plastic transparent base material (JP 5-283889).
However, the above-mentioned conventional techniques have the following problems, respectively:
(1) With this structure in which the transparent conductive film is laminated on the transparent base material, it is difficult to satisfy both visible light transmittance and electromagnetic radiation shielding performance. Also, when this transparent electromagnetic radiation shielding sheet is used in a plasma display device which emits a particularly strong electromagnetic radiation, sufficient electromagnetic radiation shielding performance cannot be obtained. (2) With this structure in which the conductive fabric is laminated on the transparent base material, the fabric tends to gather particles and dust thereby the visibility is degraded. (3) With this structure in which the conductive fabric is intervened between the two sheets of glass plate to integrally laminate the component materials, an attempt to make the obtained sheet light cannot be achieved because two sheets of glass plate are used therein.
Regarding the structures (4) and (5) above, sufficient visible light transmittance and electromagnetic radiation shielding performance may be obtained by controlling the line widths and line intervals of the conductive mesh or the conductive pattern. It may also be possible to obtain a transparent electromagnetic radiation shielding sheet that is relatively light and has various functions by laminating a glass or plastic transparent base material and various polymeric function film having a function such as antireflection, antiglare, near infrared ray absorption, etc. However, when these transparent electromagnetic radiation shielding sheets are placed under the condition with high temperature and high moisture for a long period of time, the conductive mesh or the conductive pattern of the metal corrodes. As a result, the visibility of the transparent electromagnetic radiation shielding sheet is degraded.
It is an object of the present invention to provide a transparent electromagnetic radiation shielding sheet that has both sufficient visible light transmittance and electromagnetic radiation shielding performance and that is also light, excellent in durability and is favorably used in various display devices.
It is another object of the present invention to provide a method of producing such transparent electromagnetic radiation shielding sheet.
It is a further object of the present invention to provide a display device such as a plasma display device and a CRT (cold-cathode ray tube) having the transparent electromagnetic radiation shielding sheet which is placed on the front surface of the display panel thereof.
In their attempts to achieve these objects, the inventors learned that hot melt adhesive resins such as ethylene-vinylacetates and polyesters are generally used for a transparent electromagnetic radiation shielding sheet because they have excellent forming ability, visible light transmittance and adhesiveness to glass and plastics. They also learned that when these hot melt adhesive resins are placed under conditions of high temperature and high moisture for a long period of time, organic acid is produced by hydrolysis, and the conductive mesh or the conductive pattern having a metal corrodes. In addition, the ionized metals of the conductive mesh or the conductive pattern form complexes that exhibit color. As a result, the visibility of the transparent electromagnetic radiation shielding sheet is degraded.
Through their further studies, the inventors have found that a transparent electromagnetic radiation shielding sheet having excellent performance and capabilities as discussed above can be obtained by using a hot melt adhesive resin comprising a resin having a structure where organic acid is not produced by hydrolysis. The present invention has been accomplished based on these findings.
Specifically, the present invention provides:
(1) A transparent electromagnetic radiation shielding sheet comprising:
a transparent base material,
a mesh-like conductive material having a metal, and
a resin layer contacting at least one surface of said mesh-like conductive material,
wherein said resin layer comprises a hot melt adhesive resin having more than 80 weight % of at least one of the repetition units represented by the following generic formulae (I), (II) and (III):
xe2x80x94(xe2x80x94CH2xe2x80x94CH(R1)xe2x80x94)xe2x80x94xe2x80x83xe2x80x83(I)
(wherein R1 represents a hydrogen atom or a methyl group)
xe2x80x94(xe2x80x94CH2xe2x80x94C(R2)(COOxe2x80x94R3)xe2x80x94)xe2x80x94xe2x80x83xe2x80x83(II)
(wherein R2 represents a hydrogen atom or a methyl group, and R3 represents an alkyl group having from 1 to 4 carbon atoms) 
(wherein R4 represents a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms);
(2) a method of producing a transparent electromagnetic radiation shielding sheet in which a mesh-like conductive material having a metal and a hot melt adhesive film having more than 80 weight % of at least one of the repetition units represented by the generic formulae (I), (II) and (III) are laminated on a transparent base material by thermal pressing so that the hot melt adhesive film is melted thereby the component materials are integrally laminated; and
(3) a display device having the transparent electromagnetic radiation shielding sheet which is placed on the front surface of the display panel thereof.